Radiopaque super-elastic intravascular stent

ABSTRACT

The intravascular stent is formed from a composite wire includes an inner core of radiopaque metal, a polymer layer coaxially disposed about the inner core, and an outer metal layer coaxially disposed about the polymer layer. The intermediary polymer layer acts as a barrier material between the inner core and the outer sheath, so that the inner core and outer sheath may be made of dissimilar metallic layers, and the intermediary polymer layer will prevent a galvanic reaction between the inner core and the peripheral metal layer. The intravascular stent has ends flared radially outwardly to prevent radially and longitudinally inward deformation of the ends of the stent when the stent is disposed in a desired location in a patient&#39;s vasculature.

CROSS-REFERENCES TO RELATED APPLICATIONS INVENTION

This application is a divisional of co-pending application Ser. No.11/970,338 filed on Jan. 7, 2008.

BACKGROUND OF THE INVENTION

This invention relates generally to implantable vasoocclusive devicesfor interventional therapeutic treatment or vascular surgery, and moreparticularly concerns a radiopaque super-elastic intravascular stentformed from a composite wire with enhanced radiopacity and increasedcorrosion resistance. The intravascular stent has superelastic or shapememory properties and improved radiopaque properties for visibledetection under fluoroscopy, and the ends of the stent are flaredradially outwardly to prevent radially and longitudinally inwarddeformation of the ends of the stent when the stent is stretched ordisposed in a desired location in a patient's vasculature.

Vasoocclusive devices are therapeutic devices that are placed within thevasculature of the human body, typically via a catheter, either to blockthe flow of blood through a vessel making up that portion of thevasculature through the formation of an embolus or to form such anembolus within an aneurysm stemming from the vessel. The vasoocclusivedevices can take a variety of configurations, and are generally formedof one or more elements that are larger in the deployed configurationthan when they are within the delivery catheter prior to placement. Onewidely used vasoocclusive device is a helical wire coil having adeployed configuration that may be dimensioned to engage the walls ofthe vessels.

The vasoocclusive devices, which can have a primary shape of a coil ofwire that is then formed into a more complex secondary shape, can beproduced in such a way that they will pass through the lumen of acatheter in a linear shape and take on a complex shape as originallyformed after being deployed into the area of interest, such as ananeurysm. A variety of detachment mechanisms to release the device froma pusher have been developed and are known in the art.

For treatment of areas of the small diameter vasculature such as a smallartery or vein in the brain, for example, and for treatment of aneurysmsand the like, microcoils formed of very small diameter wire are used inorder to restrict, reinforce, or to occlude such small diameter areas ofthe vasculature. A variety of materials have been suggested for use insuch microcoils, including nickel-titanium alloys, copper, stainlesssteel, platinum, tungsten, various plastics or the like, each of whichoffers certain benefits in various applications. Nickel-titanium alloysare particularly advantageous for the fabrication of such microcoils, inthat they can have super-elastic or shape memory properties, and thuscan be manufactured to easily fit into a linear portion of a catheter,but attain their originally formed, more complex shape when deployed.However, nickel-titanium alloy wires are also not radiopaque in smalldiameters, and a single nickel-titanium wire would need to beapproximately 0.012 inches in diameter to be even slightly radiopaque.However, such a thickness of a single nickel-titanium wire wouldunfortunately also be relatively stiff and possibly traumatic to theplacement site, particularly if used for treatment of delicate andalready damaged areas of the small diameter vasculature such as ananeurysm in an artery or vein in the brain, for example.

One known type of stent includes a metal filament material formed of ametal outer member and an inner core formed of a different metal thanthe outer member. Another type of stent is formed of multiple filaments,each of which is a composite including a central core formed of aradiopaque and relatively ductile material such as tantalum or platinumallowing in vivo imaging of the stent, and an outer case formed of arelatively resilient material, such as a cobalt/chromium based alloy. Anintermediate barrier layer of tantalum, niobium or platinum may beplaced between the case and core, when the core and case materials wouldbe incompatible if contiguous, due to a tendency to form intermetallics.A radiopaque case may surround the core, or to improve compatibility, abiocompatible cover layer, such as one or more of tantalum, platinum,iridium, stainless steel, niobium and titanium can surround the case.

Another type of endoprosthesis in the form of an elongated wire memberis known that includes a central cylindrical or tubular core and anouter tubular sheath. An intermediate tubular layer may be disposedbetween the inner tubular layer and the outer tubular layer. The tubemay include outer and inner layers formed of one material such ascobalt, carbon, manganese, silicon, phosphorus, sulfur, chromium,nickel, molybdenum, titanium, iron, alloys thereof and combinationthereof, and an intermediate layer between the outer and inner layersformed of another material, such as gold, platinum, tantalum, iridium,tungsten, and alloys thereof and combination thereof.

Another type of stent preform includes an elongated metal core of ashape-memory alloy with a solid cross section, and a hollow outer sheathmade of a biocompatible polymer such as a heat-shrinkable polymermaterial or polymer tape to prevent the core from directly contactingthe body lumen. In another type of stent perform, an intermediate sleeveof a lubricious lining is disposed between the core and outer sheath.

Another type of stent is known that is made from multiple knitted orbraided wire strands made of materials such as stainless steel,tungsten, titanium, nickel titanium alloy, gold or silver, coated on theoutside with a biocompatible fluoropolymer.

While nickel-titanium wire such as nitinol wire has important shapememory and superelastic properties that are useful in vasoocclusivedevices and stents, this material is not very radiopaque, so that itwould be desirable to utilize a more radiopaque material that can bevisualized under fluoroscopy. More radiopaque materials typically do nothave shape memory and superelastic properties suitable for forming invasoocclusive devices and stents, and combining such radiopaquematerials with nickel-titanium wire such as nitinol wire are typicallyprone to galvanic corrosion, resulting in failure or compromise of thelarger wire or the larger assembled system. It has also been found thatwhen an intravascular stent is stretched longitudinally, the stent willnaturally shrink in diameter, but will not shrink uniformly, in that theends of the stent will commonly shrink in diameter to a greater extentthan the diameter of a central body portion of the stent shrinks,resulting in a condition referred to as “fishmouthing” of the stent.

It would thus be desirable to provide an intravascular stent formed froma structural element that offers the advantages of a shape memory alloysuch as a nickel-titanium alloy, and that incorporates radiopaquematerial, so that the intravascular stent can be visualized underfluoroscopy, and that is not subject to galvanic corrosion during use ofthe device. It would also be desirable to provide an intravascular stentthat will resist radially and longitudinally inward deformation of theends of the stent when the stent is stretched or disposed in a desiredlocation in a patient's vasculature. The present invention meets theseand other needs.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the present invention provides for agenerally tubular intravascular stent with a plurality of end loopportions at opposing first and second ends of the stent, and anintermediate tubular body portion formed of a plurality of intermediatecircumferential loops between the plurality of end loop portions. Theintermediate tubular body portion has a first diameter, an enlargedfirst end and an enlarged opposing second end, and the enlarged firstand second ends have a second diameter greater than the first diameterof the intermediate tubular body portion. In a presently preferredaspect, a plurality of the end loop portions flare radially outward withrespect to the intermediate tubular body portion of the stent. Inanother preferred aspect, the plurality of end loop portions and theplurality of intermediate circumferential loops of the intermediatetubular body portion are formed from a single spirally wound compositewire. The composite wire has a first free end and a second free endplaced in close proximity to each other, and a short segment of heatshrink tubing is used to capture the first and second free ends togetherto prevent the free ends of the composite wire from extending away fromthe body of the stent. The intravascular stent takes on a linear shapewhen stretched, without the ends shrinking to a diameter less than thediameter of the central body of the stent.

In another presently preferred aspect, the composite wire may be formedas a cylindrical wire, and includes an elongated inner core having aselected length and formed from a radiopaque metal, an intermediatepolymer layer coaxially disposed immediately adjacent to and surroundingthe inner core, and an outer metal layer coaxially disposed immediatelyadjacent to and surrounding the polymer layer. The radiopaque metal maybe selected from the group consisting of platinum, tantalum, gold, andcombinations thereof, and the inner core is typically cylindrical,although other shapes may be suitable for forming the inner core. In apreferred aspect, the inner core is disposed centrally along alongitudinal axis of the composite wire.

In another preferred aspect, the polymer layer may be formed from apolymer selected from the group consisting of polytetrafluoroethylene,poly-para-xylylene, a fluorine substituted poly-para-xylylene, andcombinations thereof, while the outer metal layer may be formed of asuperelastic alloy, such as nitinol, for example. In another aspect, theinner core and outer sheath may be made of dissimilar metals.

In another aspect, the present invention provides for a cylindricalmandrel including a cylindrical main body having first and secondopposing ends and a longitudinal axis, a first set of four orthogonallyarranged pegs extending from the cylindrical main body at the first endof the cylindrical main body, and a second set of four orthogonallyarranged pegs extending from the cylindrical main body at the second endof the cylindrical main body. A first conical end cap is mounted to thefirst end of the cylindrical main body, and a second conical end capmounted to the second end of the cylindrical main body. In a presentlypreferred aspect, the first and second conical end caps have conicallytapered surfaces forming a tapered angle at the first and second ends ofthe cylindrical main body, and in another aspect the tapered angle isabout 30° with respect to the longitudinal axis of the cylindrical mainbody.

In another presently preferred aspect, the invention provides for amethod for forming an intravascular stent, including the steps ofwinding a single composite wire about a first peg of the first set ofpegs of the mandrel at the first end of the mandrel to form a first endloop portion at the first end of the stent, and thereafter transitioningto form an intermediate circumferential loop; winding the composite wireabout a first peg of the second set of pegs at the second end of thecylindrical mandrel to form a first end loop portion at the second endof the stent, and thereafter transitioning to form an intermediatecircumferential loop; and repeating these steps to continue sequentiallyto form a plurality of intermediate circumferential loops between aplurality of end loop portions at the opposing first and second ends ofthe mandrel.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description and the accompanyingdrawings, which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a selected length of a composite wireaccording to the present invention.

FIG. 2 is a cross sectional view of the composite wire taken along line2-2 of FIG. 1.

FIG. 3 is a top plan view of a radiopaque super-elastic intravascularstent formed from a composite wire according to the present invention.

FIG. 4 is a side elevational view of the radiopaque super-elasticintravascular stent of FIG. 3.

FIG. 5 is an end view of the radiopaque super-elastic intravascularstent of FIG. 3.

FIG. 6 is a side elevational view of a mandrel for winding theradiopaque super-elastic intravascular stent of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is illustrated in the drawings, which are provided for the purposesof illustration and not by way of limitation, the invention is embodiedin a radiopaque super-elastic intravascular stent 8, illustrated inFIGS. 3-6, formed from a composite wire for forming a vascularinterventional device, such as intravascular stents, embolization coilsand guidewires, for example. Referring to FIGS. 1 and 2, the compositewire 10 includes an elongated inner core 12 having a selected length andformed from a radiopaque metal, such as, but not limited to, platinum,tantalum, gold, or combinations thereof, for example. The inner core ispreferably cylindrical in configuration although other shapes may beused in forming the core, and the inner core is preferably disposedcentrally along a longitudinal axis 14 of the composite wire, althoughalternatively the inner core may be displaced from the centrallongitudinal axis of the composite wire.

Immediately adjacent to and surrounding the inner core is anintermediate polymer layer 16 that is preferably coaxially disposedabout the inner core. The intermediate polymer layer is formed by a thincontinuous polymeric layer of material such as, but not limited to,polytetrafluoroethylene (PTFE), poly-para-xylylene (parylene), or itshigh temperature resistant derivatives, such as a fluorine substitutedpoly-para-xylylene (parylene HT), for example, or combinations thereof.

Immediately adjacent to and surrounding the intermediate polymer layeris an outer metal layer 18 that is preferably coaxially disposed aboutthe intermediate polymer layer. In a presently preferred aspect, theinner core and the outer metal layer are made of dissimilar metals, andthe outer metal layer is formed of a superelastic alloy, such asnitinol, for example, although other metallic materials may be used forforming the outer metal layer. The intermediate polymer layeradvantageously insulates the metallic core and outer metal layer fromgalvanic corrosion.

Referring to FIGS. 3-5, the intravascular stent is formed in a generallytubular shape having an intermediate tubular body portion 20 having afirst diameter D₁, an enlarged first end 22 and an enlarged opposingsecond end 24. The enlarged first and second ends preferably have asecond diameter D₂ greater than the first diameter of the intermediatetubular body portion. The intravascular stent is currently preferablyformed from a single composite wire spirally wound to form a pluralityof intermediate circumferential loops 26 between a plurality of end loopportions 28 at the opposing first and second ends of the stent. Inanother presently preferred aspect, a plurality of the end loop portions30 a, 30 b, 30 c, 30 d flare radially outward with respect to theintermediate tubular body portion of the stent. The flared intravascularstent typically takes on a linear shape when stretched, without the endsshrinking to a diameter less than the diameter of the central body ofthe stent.

With reference to FIG. 4, the composite wire that forms theintravascular stent has a first free end 32 and a second free end 34that are placed in close proximity to each other, and are capturedtogether within a short segment of heat shrink tubing 36 to prevent thefree ends of the composite wire from extending away from the body of thestent.

As is illustrated in FIG. 6, the intravascular stent is formed bywinding a length of the single composite wire spirally about acylindrical mandrel 40 having a first set 42 of four orthogonallyarranged pegs 44 a, 44 b, 44 c, 44 d (hidden) extending from the mandrelat the first end 46 of the mandrel, and a second set 48 of fourorthogonally arranged pegs 50 a, 50 b, 50 c, 50 d (hidden) extendingfrom the mandrel at the second end 52 of the mandrel. A first conicalend cap 54 and a second conical end cap 56 are mounted to the first andsecond ends of the mandrel. The first and second conical end caps haveconically tapered surfaces 58, 60 forming an angle a typically of about30° with respect to the longitudinal axis 62 of the mandrel at the firstand second ends of the mandrel, to provide radially outwardly flaringsurfaces for shaping the outwardly flaring end loops of theintravascular stent.

According to the method of the invention, a single composite wire iswound about a first peg 44 b of the first set of pegs at the first endof the mandrel to form a first end loop portion 64 at the first end ofthe stent, thereafter transitioning to form an intermediatecircumferential loop 66. The composite wire is then wound about a firstpeg 50 c of the second set of pegs at the second end of the mandrel toform a first end loop portion (hidden) at the second end of the stent,thereafter transitioning to form another intermediate circumferentialloop, and so on, continuing sequentially in this manner thereafter toform the plurality of intermediate circumferential loops between aplurality of end loop portions at the opposing first and second ends ofthe stent. As will be readily apparent, the winding may begin at anystage, such as by first winding about the cylindrical mandrel to form anintermediate circumferential loop, followed by winding about a peg at anend of the mandrel to form an end loop portion, and so on sequentiallyin this manner.

The radiopaque super-elastic intravascular stent of the presentinvention is designed to be deployed intravascularly without thenecessity of balloons or other expansive elements, and can be deployedfrom a guiding catheter directly into the area to be treated. Theintravascular device of the present invention is particularly useful fortreatment of damaged arteries incorporating aneurysms and the like,particularly those which are treatable by the use of embolic coils orother embolic devices or agents used to occlude the aneurysm. Moreparticularly, the intravascular stent of the invention is particularlywell adapted to use with the types of catheters used to place suchembolic coils in aneurysms, and the device may be used to reinforce thearea in the vicinity of an aneurysm while allowing placement of one ormore embolic coils through the gaps in the stent, and while assisting inthe retention of the embolic devices within a dome of the aneurysm.

It will be apparent from the foregoing that while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

1. A composite wire for forming a vascular interventional device,comprising: an elongated inner core having a selected length and formedfrom a radiopaque metal; an intermediate polymer layer disposedimmediately adjacent to and surrounding the inner core; and an outermetal layer disposed immediately adjacent to and surrounding the polymerlayer.
 2. The composite wire of claim 1, wherein the radiopaque metal isselected from the group consisting of platinum, tantalum, gold, andcombinations thereof.
 3. The composite wire of claim 1, wherein theinner core is cylindrical.
 4. The composite wire of claim 1, wherein theinner core is disposed centrally along a longitudinal axis of thecomposite wire.
 5. The composite wire of claim 1, wherein the polymerlayer is formed from a polymer selected from the group consisting ofpolytetrafluoroethylene, poly-para-xylylene, a fluorine substitutedpoly-para-xylylene, and combinations thereof.
 6. The composite wire ofclaim 1, wherein the outer metal layer is formed of a superelasticalloy.
 7. The composite wire of claim 1, wherein the outer metal layeris formed of a nickel-titanium alloy.
 8. The composite wire of claim 1,wherein the inner core and outer sheath are made of dissimilar metals.9. The composite wire of claim 1, wherein the composite wire is formedas a cylindrical wire.
 10. A composite wire for forming a vascularinterventional device, comprising: an elongated inner core having aselected length and formed from a first metal, said elongated inner coredisposed centrally along a longitudinal axis of the composite wire, andsaid first metal being radiopaque; an intermediate polymer layercoaxially disposed immediately adjacent to and surrounding the innercore; and an outer metal layer coaxially disposed immediately adjacentto and surrounding the polymer layer, said outer metal layer beingformed of a second metal different from said first metal.
 11. Thecomposite wire of claim 10, wherein the first metal is selected from thegroup consisting of platinum, tantalum, gold, and combinations thereof.12. The composite wire of claim 10, wherein the inner core iscylindrical.
 13. The composite wire of claim 10, wherein the polymerlayer is formed from a polymer selected from the group consisting ofpolytetrafluoroethylene, poly-para-xylylene, a fluorine substitutedpoly-para-xylylene, and combinations thereof.
 14. The composite wire ofclaim 10, wherein said second metal is a superelastic alloy.
 15. Thecomposite wire of claim 1, wherein said second metal is anickel-titanium alloy.
 16. The composite wire of claim 1, wherein thecomposite wire is formed as a cylindrical wire.
 17. A composite wire forforming a vascular interventional device, comprising: an elongated innercore having a selected length and formed from a first metal selectedfrom the group consisting of platinum, tantalum, gold, and combinationsthereof, said elongated inner core disposed centrally along alongitudinal axis of the composite wire, and said first metal beingradiopaque; an intermediate polymer layer selected from the groupconsisting of polytetrafluoroethylene, poly-para-xylylene, a fluorinesubstituted poly-para-xylylene, and combinations thereof, saidintermediate polymer layer coaxially disposed immediately adjacent toand surrounding the inner core; and an outer metal layer coaxiallydisposed immediately adjacent to and surrounding the polymer layer, saidouter metal layer being formed of a superelastic second metal differentfrom said first metal.
 18. The composite wire of claim 17, wherein theinner core is cylindrical and said composite wire is cylindrical. 19.The composite wire of claim 17, wherein said superelastic second metalis a nickel-titanium alloy.
 20. The composite wire of claim 17, whereinsaid superelastic second metal is nitinol.